Power conversion device

Abstract

[Problem] To provide a power conversion device that, when a high-voltage power supply is cut off, requires neither a special discharge resistor for discharging a smoothing capacitor nor complicated winding excitation control for purposes such as preventing rotation of a motor. [Solution] A control unit 3: has a discharging circuit 26 connected to an emitter of an upper arm switching element Q1; and, when an HV battery is cut off, turns all upper and lower arm switching elements Q1-Q6 to non-conductive states and turns, to a conductive state, the upper arm switching element Q1 to which the discharging circuit 26 is connected, whereby a smoothing capacitor 6 is discharged through the discharging circuit 26 and the residual charges of the smoothing capacitor 6 are consumed through the upper arm switching element Q1 to which the discharging circuit 26 is connected.

Description

Power conversion device

[0001] The present invention relates to a power conversion device that applies a voltage to a load by an inverter circuit.

[0002] For example, a power conversion device for driving a motor of an electric compressor that constitutes an air conditioner of a vehicle is connected to a high-voltage power source (HV battery) by a connector (HV connector). If this connector comes off, there is a risk of accidents such as electric shock due to the residual charge accumulated in the smoothing capacitor. Therefore, conventionally, when the high-voltage power source is cut off due to the connector coming off or the like, measures are taken to discharge the residual charge of the smoothing capacitor.

[0003] Regarding the discharge of this residual charge, conventionally, a method of providing a discharge resistor that is always connected in parallel with the smoothing capacitor, and detecting when the high-voltage power source is cut off due to the connector coming off or the like, closing a switch, flowing the residual charge of the smoothing capacitor to the discharge resistor, and consuming it with the discharge resistor, or a method of consuming it with the winding of the motor has been proposed (see, for example, Patent Document 1 and Patent Document 2).

[0004] Japanese Patent Application Laid-Open No. 2021-530188, Japanese Patent No. 7221632

[0005] However, in the method of always connecting the above-described discharge resistor, since the discharge resistor is constantly connected in parallel with the smoothing capacitor, useless power that does not contribute to the operation of the electric compressor is consumed by the discharge resistor even during normal operation when the high-voltage power source is connected. In particular, in recent years, since the high-voltage power source has been further increased in voltage, it has been necessary to increase the discharge resistor, resulting in an increase in size and an increase in the power consumption of the discharge resistor during normal operation.

[0006] Regarding the problem of this discharge resistor, Patent Document 1 performs control to limit the power consumption in the discharge resistor (load resistor), but the problem of having to separately provide a discharge resistor remains. On the other hand, in Patent Document 2, since the residual charge of the smoothing capacitor is consumed by the winding of the motor, it is possible to reduce the above-described discharge resistor (discharge resistor), but there is a problem that winding energization control for not rotating the motor is required.

[0007] The present invention was made to solve the aforementioned conventional technical problems, and aims to provide a power conversion device that does not require the provision of a special discharge resistor to discharge the smoothing capacitor when the high-voltage power supply is cut off, nor does it require complex winding current control such as preventing the motor from rotating.

[0008] The power conversion device of the present invention comprises an inverter circuit connected between the power line and ground line of a high-voltage power supply, which applies voltage at the connection point of the upper arm switching elements and lower arm switching elements of each phase to a load, and a smoothing capacitor connected between the power line and ground line between the inverter circuit and the high-voltage power supply, and a control unit that controls the conduction / non-conductivity of each switching element, the control unit having a discharge circuit connected to the main electrode on the connection point side of at least one upper arm switching element, and when the high-voltage power supply is cut off, the upper arm switching element to which the discharge circuit is connected becomes conductive, thereby discharging the smoothing capacitor by the discharge circuit, and the upper arm switching element to which the discharge circuit is connected consumes the residual charge of the smoothing capacitor.

[0009] The power conversion device of the second invention, in addition to the above invention, is equipped with a discharge power supply for applying a predetermined conduction voltage to the control electrode of an upper arm switching element to which a discharge circuit is connected, and the discharge circuit is characterized by having a series circuit of a discharge current limiting resistor and a discharge switch connected between the main electrode on the connection point side of the upper arm switching element and the ground line.

[0010] The power conversion device of the third invention, in addition to the present invention, is equipped with a discharge power supply for applying a predetermined conduction voltage to the control electrode of an upper arm switching element to which a discharge circuit is connected, wherein the discharge circuit has a series circuit of a discharge current limiting resistor and a diode connected to the main electrode on the connection point side of a plurality of upper arm switching elements, and a discharge switch connected between each series circuit and the ground line, and the diode is oriented forward on the discharge switch side.

[0011] The power conversion device of the fourth invention is characterized in that, in addition to the second or third invention, it is equipped with a drive circuit for applying a drive voltage to the control electrode of each switching element, and the control unit outputs a drive signal to the drive circuit to control the conduction / non-conductivity of each switching element, and when the high-voltage power supply is cut off, it outputs a drive signal to the drive circuit that makes all upper arm switching elements and all lower arm switching elements non-conductive, and applies a conduction voltage from the discharge power supply to the control electrode of the upper arm switching element and discharge switch to which the discharge circuit is connected, thereby making the upper arm switching element and discharge switch conductive.

[0012] The power conversion device of the fifth invention is characterized in that, in addition to the present invention, it is equipped with a protection circuit that, when discharge by the discharge circuit is started, prohibits conduction of the lower arm switching element of the phase to which the discharge circuit is connected to the upper arm switching element.

[0013] The power conversion device of the sixth invention is characterized in that, in addition to the above invention, it includes a drive circuit for applying a drive voltage to the control electrode of each switching element, the control unit outputs a drive signal to the drive circuit to control the conduction / non-conductivity of each switching element, and the protection circuit disables the operation of the drive circuit of the lower arm switching element of the phase to which the discharge circuit is connected when discharge by the discharge circuit is started.

[0014] The seventh invention is a power conversion device characterized in that the load in the present invention is the motor of an electric compressor mounted on a vehicle.

[0015] According to the present invention, a power conversion device comprising an inverter circuit connected between the power line and ground line of a high-voltage power supply and applying voltage at the connection point of the upper arm switching elements and lower arm switching elements of each phase to a load, and a smoothing capacitor connected between the power line and ground line between the inverter circuit and the high-voltage power supply, is provided with a control unit that controls the conduction / non-conductivity of each switching element, and this control unit has a discharge circuit connected to the main electrode on the connection point side of at least one upper arm switching element, and when the high-voltage power supply is cut off, the upper arm switching element to which the discharge circuit is connected becomes conductive, thereby discharging the smoothing capacitor by the discharge circuit, and the residual charge of the smoothing capacitor is consumed by the upper arm switching element to which the discharge circuit is connected. As a result, the residual charge of the smoothing capacitor can be consumed by the upper arm switching element of the inverter circuit and the smoothing capacitor can be discharged without providing a special discharge resistor to consume the residual charge of the smoothing capacitor.

[0016] This effectively eliminates or suppresses electric shock caused by residual charge in the smoothing capacitor when the high-voltage power supply is cut off, thereby improving safety. It also resolves the increased power consumption during normal operation due to the higher voltage of the high-voltage power supply, as well as the installation space issues associated with the larger discharge resistance.

[0017] Furthermore, the configuration and control can be made simpler compared to conventional designs. For example, as in the second invention, a discharge power supply is provided to apply a predetermined conduction voltage to the control electrode of the upper arm switching element to which the discharge circuit is connected, and the discharge circuit is provided with a series circuit of a discharge current limiting resistor and a discharge switch connected between the main electrode on the connection point side of the upper arm switching element and the ground line.

[0018] Furthermore, as in the third invention, the discharge circuit is composed of a series circuit of a discharge current limiting resistor and a diode connected to the main electrode on the connection point side of a plurality of upper arm switching elements, and a discharge switch connected between each series circuit and the ground line, and the diode is configured to be forward on the discharge switch side, so that a single discharge switch can consume the residual charge of the smoothing capacitor with multiple upper arm switching elements and achieve rapid discharge.

[0019] Furthermore, as in the fourth invention, if the high-voltage power supply is cut off, the control unit outputs a drive signal to the drive circuit that deactivates all upper arm switching elements and all lower arm switching elements, and applies a conduction voltage from the discharge power supply to the control electrodes of the upper arm switching elements and discharge switches to which the discharge circuit is connected, thereby making the upper arm switching elements and discharge switches conduct, and thus the residual charge of the smoothing capacitor can be consumed by the upper arm switching elements.

[0020] Here, during discharge by the discharge circuit, if the lower arm switching element of the phase to which the discharge circuit is connected to the upper arm switching element were to become conductive, there is a risk of a short circuit occurring in the inverter circuit.

[0021] Therefore, as in the fifth invention, when discharge by the discharge circuit is started, a protection circuit is provided that prohibits conduction of the lower arm switching element of the phase to which the discharge circuit is connected to the upper arm switching element, thereby reliably eliminating the risk of short circuits in the inverter circuit.

[0022] In that case, for example, if the protection circuit, as in the sixth invention, disables the operation of the drive circuit for the lower arm switching element of the phase to which the discharge circuit is connected to the upper arm switching element, it becomes possible to reliably avoid the occurrence of a short circuit.

[0023] Furthermore, the present invention is extremely effective when applied to the motor of an electric compressor mounted on a vehicle, as in the seventh invention.

[0024] This is a functional block diagram of an electric compressor to which the present invention is applied. This is an electrical circuit diagram of a power converter according to one embodiment of the present invention. This is an electrical circuit diagram of the power converter of Figure 1 illustrating the operation when the high-voltage power supply is cut off. This is a diagram illustrating the discharge characteristics of the smoothing capacitor of Figure 3. This is an enlarged view of Figure 4. This is an electrical circuit diagram of a power converter according to another embodiment of the present invention.

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0026] Figure 1 shows the functional block of an electric compressor C that constitutes a vehicle air conditioning system as an embodiment to which the present invention is applied, and Figure 2 shows an electrical circuit diagram of one embodiment of the power converter 1 of the present invention. The power converter 1 in this embodiment is an inverter that controls the operation of the motor 2 (load) of the electric compressor C. The motor 2 is housed in the housing of the electric compressor C together with a compression mechanism (not shown), and the compression mechanism is driven by the motor 2. The power converter 1 is also provided in an inverter housing section configured in the housing of the electric compressor C.

[0027] In Figure 1, the power conversion device 1 of this embodiment comprises a control unit 3 configured with a microcomputer equipped with a microprocessor, an inverter circuit 4 for driving the motor 2, and a smoothing capacitor 6. It is connected to the HV battery 8 (DC 300V to 500V), which serves as a high-voltage power source mounted on the vehicle, via a connector 7.

[0028] Furthermore, an interlock loop 9 is installed alongside connector 7, and this interlock loop 9 is connected to control unit 3. Also, 11 is an LV battery, which serves as a low-voltage power supply for control unit 3, and this is also assumed to be mounted on the vehicle (outside the electric compressor C).

[0029] In Figure 2, the inverter circuit 4 is configured such that its input node is connected in parallel between the power line 12 and the ground line 13 of the HV battery 8 (high-voltage power supply), and it switches the voltage (DC power) of the smoothing capacitor 6 to convert it into a three-phase AC voltage, which is then supplied to the motor 2. The inverter circuit 4 in this embodiment is configured by bridging multiple switching elements (IGBTs or MOSFETs; IGBTs in this embodiment), and in this embodiment, it is equipped with six upper and lower arm switching elements Q1 to Q6 to output three-phase AC to the motor 2.

[0030] More specifically, the inverter circuit 4 comprises switching legs for each phase (U phase, V phase, W phase) formed by connecting two switching elements in series with each other. The collector (main electrode on the power supply side) of the upper arm switching element Q1 that constitutes the U phase switching leg is connected to the power supply line 12, and the emitter (main electrode on the connection point side) is connected to the collector of the lower arm switching element Q2. These connection points are connected to the U phase winding 14U of the motor 2.

[0031] Furthermore, the collector (main electrode on the power supply side) of the upper arm switching element Q3, which constitutes the V-phase switching leg, is connected to the power supply line 12, and the emitter (main electrode on the connection point side) is connected to the collector of the lower arm switching element Q4, and these connection points are connected to the V-phase winding 14V of the motor 2.

[0032] Furthermore, the collector (main electrode on the power supply side) of the upper arm switching element Q5, which constitutes the W-phase switching leg, is connected to the power supply line 12, and the emitter (main electrode on the connection point side) is connected to the collector of the lower arm switching element Q6, and these connection points are connected to the W-phase winding 14W of the motor 2.

[0033] Furthermore, each switching element Q1 to Q6 has a freewheeling diode connected in antiparallel. The inverter circuit 4 switches the DC voltage supplied from the HV battery 8 (voltage across the smoothing capacitor 6) by the conduction (ON) / non-conduction (OFF) of these switching elements Q1 to Q6, converts it into a three-phase AC voltage, and supplies it to the motor 2. When each switching element Q1 to Q6 is composed of MOSFETs, the main electrode on the power supply side becomes the drain, and the main electrode on the connection point side becomes the source. Also, in both the case of IGBTs and MOSFETs, the gate becomes the control electrode.

[0034] The smoothing capacitor 6 mentioned above is a filter that smooths the DC power input from the HV battery 8, and is connected between the power line 12 and the ground line 13 in the inverter circuit 4 and the connector 7, that is, in electrical terms, between the inverter circuit 4 and the HV battery 8.

[0035] In Figure 2, D1 to D6 are drive circuits connected to the gates (control electrodes) of each switching element Q1 to Q6 via resistors 16. These drive circuits D1 to D6 receive drive signals (gate signals) output from the inverter control circuit 17, which will be described later, and apply drive voltages (gate voltages) (including "L" level) to the gates of each switching element Q1 to Q6 based on these drive signals, thereby making them conduct / non-conductive.

[0036] Furthermore, each drive circuit D1 to D6 has an enable terminal EN, and when this enable terminal EN becomes ground potential (L), the operation of drive circuits D1 to D6 is disabled. Note that in Figure 2, only the enable terminal EN of the drive circuit D2 for the U-phase lower arm switching element Q2 is shown. Also, 18 in the figure is a resistor connected between the gate and emitter of each switching element Q1 to Q6.

[0037] The inverter control circuit 17 outputs drive signals to each drive circuit D1 to D6, thereby applying drive voltages from each drive circuit D1 to D6 to the gates of each switching element Q1 to Q6, causing them to conduct (ON) or not conduct (OFF), and applying a three-phase AC voltage to each winding 14U to 14W of the motor 2. Also, in the figure, 21 and 22 are resistors for detecting the HV voltage that are connected in series between the power line 12 and the ground line 13 on the inverter circuit 4 side from the connector 7. The voltage of the smoothing capacitor 6 is divided by resistors 21 and 22, and the terminal voltage of resistor 22 is input to the inverter control circuit 17 as the HV voltage detection signal.

[0038] In addition, in this embodiment, a discharge circuit 26 is connected to the connection point between the upper arm switching element Q1 and the lower arm switching element Q2 of the U-phase switching leg. In this embodiment, the discharge circuit 26 is composed of a series circuit of a discharge current limiting resistor 27 and a discharge switch (MOSFET in this embodiment) 28, and is connected between the connection point between the upper arm switching element Q1 and the lower arm switching element Q2 and the ground line 13.

[0039] The output of the discharge signal output circuit 31 is connected to the gate (control terminal) of the discharge switch 28 via a resistor 29. Note that 32 is a resistor connected between the gate and source of the discharge switch 28. A discharge power supply (DC 15V) 34 generated from the LV battery 11 is connected to the discharge signal output circuit 31, and the discharge signal output circuit 31 outputs and applies the voltage of the discharge power supply 34 (gate voltage) to the gate of the discharge switch 28 based on the discharge control output signal (H / L) from the inverter control circuit 17.

[0040] The output of the discharge signal output circuit 31 is further connected via a diode 33 between the gate of the upper arm switching element Q1 and the resistor 16, so that the voltage of the discharge power supply 34 can be applied as a conduction voltage to the gate of the U-phase upper arm switching element Q1. The diode 33 is oriented forward on the side where it connects to the gate of the upper arm switching element Q1 and the resistor 16.

[0041] Furthermore, the interlock loop 9 in Figure 1 is connected to the HV input shutoff / fault detection circuit 36 ​​in Figure 2. As mentioned above, the interlock loop 9 is attached to the connector 7, and when the connector 7 is connected, the loop is closed (closed circuit), and when it is disconnected, the loop is opened (open circuit). When the connector 7 is disconnected and the interlock loop 9 is opened, the level of the IL signal output by the HV input shutoff / fault detection circuit 36 ​​changes. This IL signal is then input from the HV input shutoff / fault detection circuit 36 ​​to the inverter control circuit 17 and the discharge signal output circuit 31.

[0042] The control unit 3 in this application includes at least the inverter control circuit 17, the discharge signal output circuit 31, the HV input interruption / fault detection circuit 36, and the discharge circuit 26. Furthermore, the enable terminal EN of the drive circuit D2 that drives the lower arm switching element Q2 of the U-phase switching leg described above is connected to the drain of the discharge switch 28 via a diode 37. The circuit between the enable terminal EN including this diode 37 and the drain of the discharge switch 28 constitutes the protection circuit 38 in this invention.

[0043] With the above configuration, the discharge operation of the residual charge of the smoothing capacitor 6 performed by the control unit 3 will now be explained with reference to Figures 3 to 5. In Figures 4 and 5, L1 is the voltage of the smoothing capacitor 6, L2 is the conduction voltage output from the discharge signal output circuit 31, L3 is the discharge current from the smoothing capacitor 6, L4 is the gate-emitter voltage of the upper arm switching element Q1 of the U-phase switching leg, L5 is the voltage across the discharge current limiting resistor 27, and L6 is the change in the gate current of the upper arm switching element Q1. Also, Figure 5 is an enlarged view of the time t1 portion of Figure 4.

[0044] During normal operation, a "L" discharge control output signal that deactivates the discharge signal output circuit 31 is output from the inverter control circuit 17. In this case, since the discharge signal output circuit 31 does not output the voltage of the discharge power supply 34 (DC 15V), the discharge switch 28 is non-conductive (OFF), and no current flows through the discharge circuit 26. Also, the voltage of the discharge power supply 34 (conductive voltage) is not applied to the gate of the upper arm switching element Q1 of the U-phase switching leg.

[0045] The inverter control circuit 17 that constitutes the control unit 3 outputs drive signals to each of the drive circuits D1 to D6, and applies drive voltages (including the "L" level) to the gates of the respective switching elements Q1 to Q6 by the drive circuits D1 to D6, thereby making each of the switching elements Q1 to Q6 conductive / non-conductive (switching), converting the voltage (DC voltage) of the smoothing capacitor 6 into a three-phase AC voltage, and applying it to the motor 2.

[0046] On the other hand, the inverter control circuit 17 constantly monitors the state of the interlock loop 9 based on the level of the IL signal output by the HV input cutoff / fault detection circuit 36. When the connector 7 is disconnected and becomes non-connected, and an open circuit of the interlock loop 9 is detected, it is determined that the power supply from the HV battery (high voltage power supply) 8 has been cut off, and the aforementioned IL signal is output to the inverter control circuit 17 and the discharge signal output circuit 31.

[0047] When the inverter control circuit 17 receives the IL signal, first, drive signals that make all the upper arm switching elements Q1, Q3, Q5 and all the lower arm switching elements Q2, Q4, Q6 non-conductive are output to the drive circuits D1, D3, D5, D2, D4, D6. As a result, no drive voltage is applied to the gates of all the switching elements Q1 to Q6 from the drive circuits D1 to D6.

[0048] Next, at time t1 in FIG. 4, the inverter control circuit 17 outputs a discharge control output signal of "H" to the discharge signal output circuit 31. When the discharge signal output circuit 31 receives the "H" discharge control output, it outputs the voltage of the discharge power supply 34. Since the voltage of this discharge power supply 34 is applied to the gate of the discharge switch 28, the discharge switch 28 conducts (turns on). Also, the voltage of the discharge power supply 34 is applied as a conduction voltage (L2) to the gate of the upper arm switching element Q1 of the U-phase switching leg (indicated by an arrow in FIG. 3).

[0049] When the discharge switch 28 conducts, the emitter of the upper arm switching element Q1 is connected to the ground line 13 via the discharge current limiting resistor 27. On the other hand, since a conduction voltage is applied to the gate of the upper arm switching element Q1, the voltage between the gate and emitter (L4) of the upper arm switching element Q1 rises, a gate current flows (L6), and when the gate voltage reaches the threshold value, the upper arm switching element Q1 begins to conduct (Q1 conduction start timing in FIG. 5). That is, only the upper arm switching element Q1 of the inverter circuit 4 conducts, and the other switching elements Q2 to Q6 are in a non-conducting state.

[0050] When this upper arm switching Q1 conducts, the smoothing capacitor 6 starts to discharge through the upper arm switching element Q1 by the discharge circuit 26 (indicated by an arrow in FIG. 3). Since a discharge current flows through the discharge current limiting resistor 27 due to this discharge, the emitter potential of the upper arm switching element Q1 rises. The emitter potential of the upper arm switching element Q1 rises until the conduction voltage (L2) reaches DC15V, and in accordance with the saturation of the voltage across the discharge current limiting resistor 27, the discharge current (L3) is also limited (FIG. 5).

[0051] Thereafter, as the discharge current (L3) from the smoothing capacitor 6 through the upper arm switching element Q1 continues to flow, the voltage (L1) of the smoothing capacitor 6 decreases (FIG. 4). Thus, as the discharge current flows through the upper arm switching element Q1, the residual charge of the smoothing capacitor 6 is consumed by the upper arm switching element Q1.

[0052] Furthermore, when the discharge switch 28 is turned on, an "L" level signal (L) is input to the enable terminal EN of the drive circuit D2 for the lower arm switching element Q2. As a result, the operation of the drive circuit D2 is disabled, and the lower arm switching element Q2 of the U-phase switching leg is reliably kept in a non-operating state.

[0053] Furthermore, the inverter control circuit 17 monitors the voltage of the smoothing capacitor 6 using the HV voltage detection signal. If the voltage of the smoothing capacitor 6 drops below a predetermined discharge target value due to the discharge described above, the discharge control output signal is set to "L" to deactivate the discharge signal output circuit 31. As a result, the discharge switch 28 becomes non-conductive (OFF), and the supply of conduction voltage to the gate of the upper arm switching element Q1 is stopped, thus ending the discharge operation of the smoothing capacitor 6 by the discharge circuit 26.

[0054] As described in detail above, in this embodiment, when the HV battery 8 (high-voltage power supply) is cut off, all upper arm switching elements Q1, Q3, and Q6 and all lower arm switching elements Q2, Q4, and Q6 are made non-conductive, while the upper arm switching element Q1 to which the discharge circuit 26 is connected is made conductive, causing the smoothing capacitor 6 to be discharged by the discharge circuit 26, and the residual charge of the smoothing capacitor 6 is consumed by the upper arm switching element Q1 to which the discharge circuit 26 is connected. As a result, the residual charge of the smoothing capacitor 6 can be consumed by the upper arm switching element Q1 of the inverter circuit 4, thereby discharging the smoothing capacitor 6, without providing a special discharge resistor to consume the residual charge of the smoothing capacitor 6 as in the conventional method.

[0055] This effectively eliminates or suppresses electric shock caused by residual charge in the smoothing capacitor 6 when the HV battery 8 (high-voltage power supply) is cut off, thereby improving safety. It also eliminates the increased power consumption during normal operation due to the higher voltage of the HV battery 8 (high-voltage power supply), as well as the installation space issues associated with the larger discharge resistance.

[0056] Furthermore, the configuration and control can be made simpler compared to conventional designs. In particular, as shown in the embodiment, the present invention can be realized with a simple configuration in which a discharge power supply 34 is provided to apply a predetermined conduction voltage to the gate of the upper arm switching element Q1 to which the discharge circuit 26 is connected, and the discharge circuit 26 is provided with a series circuit of a discharge current limiting resistor 27 connected between the emitter of the upper arm switching element Q1 and the ground line 13 and a discharge switch 28.

[0057] Furthermore, as in the embodiment, when discharge by the discharge circuit 26 is initiated, a protection circuit 38 is provided that prohibits conduction of the lower arm switching element Q2 of the U phase of the upper arm switching element Q1, thereby reliably eliminating the risk of short circuits in the inverter circuit 4. In particular, in this embodiment, the protection circuit 38 disables the operation of the drive circuit D2 of the lower arm switching element Q2, so that the occurrence of short circuits can be avoided more reliably.

[0058] Furthermore, the present invention is extremely effective when applied to the motor 2 of an electric compressor C mounted on a vehicle, as in the embodiment.

[0059] In the embodiment described above, the residual charge of the smoothing capacitor 6 is consumed by the upper arm switching element Q1 of the U-phase switching leg. However, it is not limited to this, and the charge may be consumed by multiple (two or three in the embodiment) upper arm switching elements. In that case, for example, the configuration shown in Figure 6 may be used. In Figure 6, elements indicated by the same reference numerals as in Figures 1 to 3 are assumed to perform the same or similar functions.

[0060] Figure 6 shows an example in which the residual charge of the smoothing capacitor 6 is consumed by two upper arm switching elements, the upper arm switching element Q1 of the U-phase switching leg and the upper arm switching element Q3 of the V-phase switching leg. In this case, the discharge circuit 26 is constructed by a series circuit of a discharge current limiting resistor 27A and a diode 41A connected to the emitter of the upper arm switching element Q1, a series circuit of a discharge current limiting resistor 27B and a diode 41B connected to the emitter of the upper arm switching element Q3, and a single discharge switch 28 connected between each series circuit and the ground line 13.

[0061] Furthermore, each diode 41A and 41B is connected such that the discharge switch 28 side is in the forward direction. In addition, protection circuits 38A and 38B are provided in the drive circuit D2 for the lower arm switching element Q2 of the U-phase switching leg and in the drive circuit D4 for the lower arm switching element Q4 of the V-phase switching leg, respectively.

[0062] In this case, the protection circuit 38A is connected between the enable terminal EN of the drive circuit D2 and the drain of the discharge switch 28, and has a diode 37A with the drain side facing forward. Similarly, the protection circuit 38B is also connected between the enable terminal EN of the drive circuit D4 and the drain of the discharge switch 28, and has a diode 37B with the drain side facing forward.

[0063] Then, the outputs of the discharge signal output circuit 31 are connected to the gates of the upper arm switching elements Q1 and Q3 and the resistor 16, respectively, via diodes 33A and 33B. As a result, when the smoothing capacitor 6 is discharged, the discharge signal output circuit 31 outputs the voltage of the discharge power supply 34, and this voltage of the discharge power supply 34 is applied to the gate of the discharge switch 28, and at the same time, the voltage of the discharge power supply 34 is applied as a conduction voltage to the gates of the upper arm switching elements Q1 and Q3 of the U-phase and V-phase switching legs.

[0064] From this point onward, the same operations as described above are performed by the upper arm switching elements Q1 and Q3 of the U-phase and V-phase switching legs, and the residual charge of the smoothing capacitor 6 is consumed by each of the upper arm switching elements Q1 and Q3. In other words, a single discharge switch 28 makes it possible to consume the residual charge of the smoothing capacitor 6 with the upper arm switching elements Q1 and Q3, thereby enabling rapid discharge.

[0065] In this case as well, when the discharge switch 28 is turned ON, an "L" level signal (L) is input to the enable terminal EN of the drive circuits D2 and D4 for the lower arm switching elements Q2 and Q4. As a result, the operation of the drive circuits D2 and D4 is disabled, and the lower arm switching elements Q2 and Q4 of the U-phase and V-phase switching legs are reliably kept inactive.

[0066] In the above embodiments, the present invention was applied to an electric compressor C mounted on a vehicle, but it is not limited to that, and the present invention is effective for power conversion devices used in various types of equipment.

[0067] C Electric Compressor D1-D6 Drive Circuit Q1-Q6 Upper and Lower Arm Switching Element 1 Power Converter 2 Motor 3 Control Unit 4 Inverter Circuit 6 Smoothing Capacitor 7 Connector 8 HV Battery (High Voltage Power Supply) 9 Interlock Loop 12 Power Line 13 Ground Line 17 Inverter Control Circuit 26 Discharge Circuit 27, 27A, 27B Discharge Current Limiting Resistor 28 Discharge Switch 31 Discharge Signal Output Circuit 34 Discharge Power Supply 36 HV Input Shutoff / Fault Detection Circuit 38, 38A, 38B Protection Circuit

Claims

1. A power conversion device comprising an inverter circuit connected between the power line and ground line of a high-voltage power supply, which applies voltage to a load at the connection point of the upper arm switching elements and lower arm switching elements of each phase, and a smoothing capacitor connected between the power line and ground line between the inverter circuit and the high-voltage power supply, wherein the power conversion device comprises a control unit that controls the conduction / non-conductivity of each switching element, the control unit having a discharge circuit connected to the main electrode on the connection point side of at least one of the upper arm switching elements, and when the high-voltage power supply is interrupted, the upper arm switching element to which the discharge circuit is connected becomes conductive, thereby discharging the smoothing capacitor by the discharge circuit, and the upper arm switching element to which the discharge circuit is connected consumes the residual charge of the smoothing capacitor.

2. The power conversion device according to claim 1, comprising a discharge power supply for applying a predetermined conduction voltage to the control electrode of the upper arm switching element to which the discharge circuit is connected, wherein the discharge circuit has a series circuit of a discharge current limiting resistor and a discharge switch connected between the main electrode on the connection point side of the upper arm switching element and the ground line.

3. The power conversion device according to claim 1, comprising a discharge power supply for applying a predetermined conduction voltage to the control electrode of an upper arm switching element to which the discharge circuit is connected, wherein the discharge circuit comprises a series circuit of a discharge current limiting resistor and a diode connected to the main electrode on the connection point side of a plurality of upper arm switching elements, and a discharge switch connected between each series circuit and the ground line, wherein the diode is oriented forward on the discharge switch side.

4. The power conversion device according to claim 2 or 3, comprising a drive circuit for applying a drive voltage to the control electrode of each switching element, wherein the control unit outputs a drive signal to the drive circuit to control the conduction / non-conductivity of each switching element, and when the high-voltage power supply is cut off, outputs a drive signal to the drive circuit to make all of the upper arm switching elements and all of the lower arm switching elements non-conductive, and applies a conduction voltage from the discharge power supply to the control electrode of the upper arm switching element to which the discharge circuit is connected and the discharge switch, thereby making the upper arm switching element and the discharge switch conductive.

5. The power conversion device according to claim 1, further comprising a protection circuit that, when discharge by the discharge circuit is initiated, prohibits conduction of the lower arm switching element in the phase to which the discharge circuit is connected to the upper arm switching element.

6. The power conversion device according to claim 5, further comprising a drive circuit for applying a drive voltage to the control electrode of each switching element, wherein the control unit outputs a drive signal to the drive circuit to control the conduction / non-conductivity of each switching element, and the protection circuit disables the operation of the drive circuit of the lower arm switching element in the phase to which the discharge circuit is connected when discharge by the discharge circuit is started.

7. The power conversion device according to claim 1, characterized in that the load is the motor of an electric compressor mounted on a vehicle.

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